The CyberKnife system uses Synchrony Motion Tracking to compensate for respiratory motion. This complex radiotherapy system needs independent performance verification to assure safe treatments. In this work, the RADPOS 4D dosimetry system is used to verify CyberKnife's motion tracking and delivered dose. RADPOS motion measurements are compared with Synchrony log files containing internal metal fiducial positions determined using orthogonal kV x-ray imaging, and external LED marker positions determined using a stereoscopic camera system. RADPOS dose measurements are compared with radiochromic film measurements and treatment planning system calculations. The standard deviation of the differences between RADPOS and LED measurements or RADPOS and fiducial measurements were <1 mm along all directions of motion. Percent comparisons between the treatment planning system, RADPOS, and film dose values were mostly within 2 standard deviations of experimental uncertainties. This work demonstrates that RADPOS is a useful tool for the independent quality assurance of CyberKnife treatments.